This invention is related to the fuel supply for internal combustion engines and, more particularly, to a fuel injector having two active control valves to control needle valve motion. One control valve is used to control the injection pressure process. The second control valve is used to directly control the fuel injector needle valve. Depending on the coordination between two control valves, different injection characteristics are obtained as desired.
A hydraulically-actuated, electronically-controlled, unit injector (HEUI), of the type described in U.S. Pat. No. 5,181,494 and in SAE Technical Paper Series 930270, HEUIxe2x80x94A New Direction for Diesel Engine Fuel Systems, S. F Glassey, at al, March 1-5, 1993, which are incorporated herein by reference, is depicted in prior art FIG. 1.
The prior art HEUI 200 is depicted in prior art FIG. 1. HEUI 200 consists of four main components: (1) control valve 202; (2) intensifier 204; (3) nozzle 206; and (4) injector housing 208.
The purpose of the control valve 202 is to initiate and end the injection process. Control valve 202 is comprised of a poppet valve 210, and electric control 212 having an armature and solenoid. High pressure actuating oil is supplied to the lower seat 214 of the valve 210 through oil passageway 216. To begin injection, the solenoid of electric control 212 is energized, moving the poppet valve 210 upward off the lower seat 214 to the upper seat 218. This action admits high pressure oil to the spring cavity 220 and the passage 222 to the intensifier 204. Injection commences and continues until the solenoid of the control 212 is de-energized and the poppet 210 moves from the upper seat 218 to lower seat 214. Oil and fuel pressure decrease as spent actuating oil is ejected from the injector 200 through the open upper seat oil discharge 224 to the valve cover area (not shown) of the internal combustion engine.
The middle segment of the injector 200 is comprised of the hydraulic intensifier piston 236, the plunger 228, the plunger chamber 230, and the plunger return spring 232.
Intensification of the fuel pressure to desired injection pressure levels is accomplished by the ratio of areas between the upper surface 234 of the intensifier piston 236 and the lower surface 238 of the plunger 228. The intensification ratio can be tailored to achieve desired injection characteristics. Injection begins as high pressure actuating oil is supplied to the upper surface 234 of the intensifier piston 236. Fuel is admitted to the plunger chamber 230 (formed in part by lower surface 238) through passageway 240 past check valve 242.
As the piston 236 and plunger 228 move downward, the pressure of the fuel in plunger chamber 230 below the lower surface 238 of the plunger 228 rises. High pressure fuel flows in passageway 244 past check valve 246 to act upward on needle valve 250. The upward force opens needle valve 250 and fuel is discharged from orifice 252. The piston 236 continues to move downward until the solenoid of the control 212 is de-energized, causing the poppet 210 to return to the lower seat 214, thereby blocking actuating oil flow. Oil pressure above the intensifier piston is now vented to the ambient through drain passage 224. The plunger return spring 232 returns, the piston 236 and plunger 228 to their initial positions. As the plunger 228 returns, the plunger 228 draws replenishing fuel into the plunger chamber 230 across ball check valve 242.
The nozzle 206 is typical of other diesel fuel system nozzles. The valve-closed-orifice style is shown, although a mini-sac version of the tip is also available. Fuel is supplied to the nozzle orifice 252 through internal passages. As fuel pressure increases, the nozzle needle valve 250 is lifted from the lower seat 254 (compressing spring 256), thereby opening the needle valve 250 and causing fuel injection to occur. As fuel pressure decreases at the end of injection, the spring 256 returns the needle valve 250 to its closed position on the lower seat 254.
The HEUI Intensifier System
For all unit injectors in production today, there is only one active control valve in each injector. Fuel injectors are typically of the common rail or intensifier types. The common rail type (Lucas and Bosch type systems) has a very high pressure fuel rail that supplies fuel to the injector at a pressure ready for injection, on the order of 20,000 psi. The intensifier injector (HEUI type) includes an intensifier plunger in the injector itself to bring low supply fuel pressure to a desired injection pressure level internally. This process is as described above.
One of very desired characteristics of the HEUI intensifier system is its similarity in performance to the Bosch type pump and nozzle injection system (cam system), where injection pressure is gradually built up during an injection event. This gradual building up process produces a generally triangle shaped rate-of-injection single shot injection event where the initial portion of the injection pressure rate trace rises gradually, as distinct from a sharp rising. See FIG. 3, case 4. This type of injection rate trace provides a benefit to reduce NOx emissions at high speed engine operation. This is a very special feature of the intensifier system. Common rail systems can not produce this feature.
In the HEUI injector concept shown in U.S. Pat. No. 5,460,329, pilot injection is produced through double action of a single spool digital control valve. The result is similar to the solid line injection event depicted in FIG. 3, case 1. The entire injection event, having a pilot injection event preceding a main injection event, is considered as two independent, pulse-width-controlled, single injection events occurring in very close sequence. The pilot portion of injection is a single shot of injection but with very short pulse width. With this philosophy, the intensifier chamber pressure is vented to terminate the pilot injection at the end of the pilot injection event and recharged again to start the main injection.
The HEUI B injector, described in U.S. Pat. No. 5,682,858, improves its performance by using direct control of the needle valve. However, the intensifier is also passively controlled by the same control valve. The actuation process is not totally independent of needle timing control. This type of injector cannot have fully flexible injection timing and rate shaping control across the whole engine speed and load range. It may have difficulty producing certain dwell and certain pilot injection size when the actuation pressure is mismatched. Another desirable characteristic of the intensifier system is its product safety. High injection pressure is developed within the injector only during a short period during the engine cycle, only during the time window where injection events are going to occur, as distinct from a high pressure common rail system. The injector stays in a low pressure environment for the rest of the engine cycle. Additionally, there is no external plumbing required to transport fuel from a high pressure pump to the injector as in the common rail system. Compared to the common rail system, the intensifier system demonstrates a much superior advantage that appeals to a large number of engine manufacturers.
Common Rail Systems (Lucas and Bosch Type Systems)
The common rail fuel system is very different from the previously described injectors that incorporate an intensifier system. In the common rail system, the injector is not responsible for the injection pressure development process. Rather, the high pressure fuel, on the order of 20,000 psi is delivered to the injector from the common rail ready for injection into the combustion chamber of an engine. The injector has direct timing control of the injector needle valve with a relatively simple timing control process to produce the desired pilot injection and injection event dwell (duration). Injection timing and duration are purely a timing issue. In any unit injection system, the speed of control valve response is considered as the most crucial element and the limiting factor for achieving small pilot and small dwell size especially under high engine speed and high injection pressure operation conditions. Using one control valve to handle both pressure and timing, as in the intensifier system, can be very challenging and limiting. Thus, decoupling the pressure development process from the timing control process becomes a necessary step to further improve injection system performance in the future. The common rail system by its nature is decoupled, being responsible only for timing. For this reason, the common rail system has much superior control of the pilot size and dwell duration due to its direct needle control and independent fuel pressure control outside of the injector as compared to the intensifier system.
Both the Lucas and the Bosch type unit injectors have only one active control valve on each injector. For both of them, the single control valve is used to directly control the timing of the needle valve opening and closing. The sole function of the control valve in a common rail system is control of the timing of injection events (e.g., starting, ending and duration of the injection).
Timing control of the fuel injector is highly dependent on the response time of the control valve. For this reason, the Lucas type system apparently has better response than the Bosch type system due to its faster response of the control valve.
The present invention injector has the advantages of both the intensifier system and the common rail system, while substantially avoiding the problems of the two systems as indicated below.
(1) Decoupling The Injection Pressure Preparation From Timing Control, Without Going To A High Pressure Common Rail.
This is achieved by having two active control valves in one unit injector of the intensifier type. One control valve (the pressure control valve) is on the actuation liquid side and other control valve (the timing control valve) is on the high pressure fuel side. In order to maintain the advantages of the intensifier system, the pressure control valve is used to control the pressure actuation process. The pressure control valve is responsible for opening up the window of injection opportunity. The timing control valve is responsible for controlling when and how long the injection event takes place within the window of opportunity. This two control valve system is the marriage between the intensifier system and the common rail system. The present invention keeps the advantages of both systems (intensifier and common rail) and provides the opportunity to eliminate the undesired characteristics of each of the systems alone. Since the injector of the present invention has two active control valves, coordination of the control schedule between two valves can produce markedly different and desirable injection characteristics. More particularly, the pressure control valve is used to define the window of operation during which the actuation pressure will be used. The timing control valve is responsible within the window for the precise control of injection timing events and duration, such as start of injection, end of injection, timing of interruption and duration of interruption.
(2) The Pilot Injection Process Of The Present Invention Is Accomplished By Controlled Interruption Of A Normal Injection Event.
With the present invention, an injection event, including pilot injection and/or rate shaping, is considered as a single shot injection event, but with a certain duration of interruption. The duration of interruption (dwell) is effected by the timing control valve and is the consequence of dwell. When the interruption (dwell) is short, it results in a rate shaping injection. See FIG. 3, case 5 and FIG. 4, case 5. When the interruption is long, it causes split or pilot injection. See FIG. 3, case 1 and FIG. 4, case 3. Without any interruption, the injection is a normal single shot. See FIG. 3, case 4 and FIG. 4, case 1. But with interruption, depending on the duration of interruption (dwell), the injection flow curve can be formed to provide rate shaping, split injection, pilot injection and more injection segments as needed. This controlled interruption to a normal injection event can happen any time during the injection event as long as actuation pressure or injection pressure exists.
(3) Independent Control Of Pilot Injection And Main Injection Within A Single Shot Injection Event.
All present unit injection systems need to achieve pilot injection and main injection by generating two independent single shot injection events. For example, the injection system described in U.S. Pat. No. 5,460,329 requires the decay of actuation pressure to define between the pilot and main injection events. In the prior art, this may be accomplished by reversal of the motion of the intensifier. Such reversal has the disadvantage of diminishing the injection pressure in the fuel injector. Once the injection pressure is developed in the fuel injector during an injection event, the injection pressure should not be destroyed for the purpose of pilot injection pressure, if possible. The total time allowed for injection to occur is too short to waste in diminishing and rebuilding injection pressure. Therefore, the concept of the present invention is to emphasize no reverse motion of the intensifier piston and plunger during pilot injection, thereby maintaining injection pressure. Dwell in the pilot injection is caused by closing the needle valve rather than by reducing or eliminating the injection pressure. The timing control valve of the present invention is used to spill part of the high pressure fuel to the back of the needle valve to force needle valve closing. This closing creates the separate pilot and main injection events while maintaining injection pressure in the injector.
(4) The Present Invention Improves The Digital Control Valve HEUI Injection System (U.S. Pat. No. 5,460,329), Making It More Efficient In Main Injection Pressure And Shorter In Duration.
This improvement is achieved in the present invention by having main injection occur under maximum injection pressure situation. Maximum injection pressure is obtained by having the full actuation pressure level acting on the intensifier piston at all times during the injection event. The intensifier chamber pressure is maintained at maximum actuation pressure, since the pressure control valve stays open all the time throughout the injection event, i.e., the plunger chamber fuel pressure then is maintained at maximum intensified level. There is no double action of the pressure control valve as in the past.
(5) Improved Response In Shaping The Injection Event As Desired.
In the present invention, the pressure control valve is much larger (in terms of flow area) than the timing control valve and is therefore much less responsive than the timing control valve. This is because the flow; rate of actuation liquid is about seven times more than the fuel injection flow rate. Therefore, with the concept of the present invention, the large pressure control valve is only operated once per injection event while the small timing control valve can be operated multiple times if needed during an injection event in order to effect the desired rate-of-injection shape. This is evident in reviewing the valve positions depicted in cases 1-5 of FIG. 4. The relatively small timing control valve has much better response than the relatively larger pressure control valve.
(6) More Varied Injection Characteristics Are Achieved With The Two Active Control Valves Of The Present Invention In One Unit Injector Of The Intensifier Type Than Can Be Achieved With A Single Control Valve.
No present fuel injection system is able to generate all the noted flexible injection characteristics without introducing significant variability from injection event to injection event and deterioration of performance. Most production injectors can only do some of the features listed in FIG. 3. All of the FIG. 3 features are attainable by the present invention. It is highly desirable that a unit injector be able to do all of these features in order to meet high emission standards, reduced noise, and improved drivability.
The present invention includes a needle valve controller for use in a fuel injector to control the opening and closing of a fuel injector needle valve, including a selectively actuatable timing control valve being in flow communication with a source of fuel under pressure and being in flow communication with a fuel injector needle valve surface, the valve being shiftable between an open and a closed disposition. A controller is operably coupled to the timing control valve for controlling the shifting of the timing control valve between the valve open and closed dispositions, opening of the timing control valve acting to port fuel under pressure to the fuel injector needle valve surface, the fuel generating a force on the fuel injector needle valve surface acting to close the fuel injector needle valve.
The present invention is further a method of defining a fuel injection event in a fuel injector having a fuel pressure intensifier, including the steps of (a) preparing fuel pressure with a fuel injection pressure control valve, and (b) controlling the timing of a fuel injection event with a fuel injection timing control valve, the fuel pressure preparation and the timing of the fuel inject event being independently controllable.